Power sources for sensors such as Geiger counter tube and ultraviolet sensing tube, using discharge tubes as their sensing elements, have commonly used supply voltages slightly lower than respective self-discharge voltages of the discharge tubes.
In general, the power source to be used for a sensor has to supply a stable operating voltage to the sensing circuit to thus keep this functionable at all times during the sensing mode of operation and waiting mode of operation for obtaining a reliable operation. Accordingly, the sensor consumes a certain amount of electric power even in the waiting mode, wherein no sensing mode occurs, to hold ready for the sensing. The sensor of discharge type has a performance characteristic such that it consumes a large amount of electric power in the sensing mode only, stores rapidly electric power for discharge concurrently with the sensing mode in order to provide for the next sensing mode, and consumes an extremely small amount of electric power in the waiting mode. Therefore, the power source to be used for a discharge type sensor is needed to be designed so as to rapidly supply a large amount of electric power only in the time of discharge in the sensing mode and supply no more than such amount of power that is consumed as a loss in the waiting mode i.e., to reduce the power consumption as a whole, with a stable voltage being supplied to the sensor, thereby enabling the sensor to operate effectively and reliably over a long period of time.